1. Technical Field
The present invention relates to an ink set and an image forming method.
2. Description of the Related Art
In recent years, as a result of ever-increasing demand for the protection of resources, protection of the environment, the enhancement of operational stability, and the like, the conversion of paints and inks into aqueous products is advancing. As in the case of oil-based paints and oil-based inks, the qualities required in aqueous paints and aqueous inks include fluidity, storage stability, glossiness of film, clarity, coloring ability, and the like. Pigments essentially have high durability and extremely excellent lightfastness and water resistance as compared with dyes due to their high crystallinity. However, compared with oil-based vehicles, most pigments have a markedly poor adaptability to aqueous vehicles with respect to pigment dispersibility and the like and therefore, satisfactory quality cannot be obtained by conventional dispersion methods. The use of various additives, for example, aqueous pigment dispersion resins or surfactants, has hitherto been studied, but an aqueous paint or an aqueous ink that satisfies all the adaptation properties described above and is comparable to existing high quality oil-based paints or high quality oil-based inks has not been obtained.
Further, concerning an ink jet ink, an ink jet ink having high penetrability into a recording medium is generally used, in consideration of its fixing rate and bleeding between colors. Therefore, when an image is formed using a plain paper, the colorant may penetrate toward the inside of the recording medium, and a sufficient amount of colorant to be fixed on the surface of the recording medium can not be secured and, as a result of which, a recorded matter having a good colorability is difficult to obtain.
In connection with the above, in order to improve dispersibility of the pigment, a pigment-dispersed ink prepared by using a graft polymer in which the main chain and the side chain have different functions such that the functions of the main chain and the side chain are separated into a hydrophilic function and a hydrophobic function has been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2005-133089). Further, in order to improve storage stability of the ink, an ink jet ink prepared by using a polymer dispersant which has a small dispersion with respect to hydrophobic group units and hydrophilic group units has been disclosed (see, for example, JP-A No. 2006-342201).